Soil nailing is a cost-effective method of in situ ground reinforcement, in which passive, or non pre-stressed reinforcing elements are installed into the ground and attached to a facing of reinforced shotcrete or concrete. The cost effectiveness of soil nailing depends in part on the ability of vertical cuts in the ground to stand unsupported for a sufficient length of time to allow erection of the face reinforcing steel and subsequent application with shotcrete. The length of time that a vertical face can stand unsupported is referred to as "stand-up time." When the stand-up time of vertical cuts at the face is limited, face stability problems do not allow economical soil nail wall construction. These situations typically require alternative, more costly wall systems, such as soldier piles, sheet piles or tieback walls.
U.S. Pat. No. 3,802,204 to Mason teaches the early use of tendon rods or dowels, inserted into an embankment to aid in the support of a temporary retaining wall, as an alternative to sheet pilings. An additional feature of the Mason '204 retaining wall is that Mason '204 teaches the use of horizontal concrete wale beams that include reinforcing rods. Mason '204 also teaches the use of pneumatically delivered concrete. Pneumatically delivered concrete is also called "shotcrete" or "gunnite," and can be fiber reinforced for additional strength. However, the wale beams of Mason '204 fail to provide any vertically oriented support for the soil reinforcing rods that extend back horizontally into the excavation. Therefore, there is a need for a retaining wall system that provides a simple and economical, vertical and horizontal support for an excavated wall.
U.S. Pat. No. 4,911,583 to Carey teaches the addition of vertical rods, drilled into the ground along the face of an excavation, to provide an improved retaining wall. The Carey '583 disclosure teaches only the use of vertical rods with soft shale rock or "stiff soil." The vertical rods are taught by Carey '583 as better able to help define the face of an excavation in these stiff soils, compared to soldier piles. Carey '583 teaches the placement of the vertical rods at two to four foot centers. This placement may eliminate the need for larger diameter soldier piles or wide soldier sheet piles. However, Carey '583 fails to teach any method that is applicable to softer soils. A retaining wall system is needed for soils that are not stable enough to remain in place with simply vertical rods and separate, conventional horizontal anchors.
U.S. Pat. No. 4,952,097 to Kulchin teaches the use of steel plates placed over the proximal ends of soil anchoring rods. The steel plates are mounted next to a grid of rebar so that the tensile strength of the soil anchors provides reenforcement to the rebar grid, which receives shotcrete to form a permanent concrete wall. FIG. 2 of Kulchin '097 shows this grid of rebar used to reinforce the concrete wall. A problem with Kulchin '097 is that the rebar grid relies on the soil anchors for substantially all of the wall's support. To provide the "permanent" retaining wall, as described by Kulchin '097, a substantial footing is also required to prevent the base of the wall from "kicking out," especially in unstable and high water content soils. The footing is a costly addition to a retaining wall. A permanent retaining wall system is needed that can shore an excavation of unstable soils without the need for additional trenching along the base of the excavated wall for receiving a large and costly foundation.
U.S. Pat. No. 5,456,544 to Barrett et al. teaches a vertical wall support system that includes a horizontal pipe extending from a vertical pipe to form an L-shaped member for supporting a wall, as shown in FIG. 17, therein. The L-shaped member of Barrett '544 requires a foundational layer of concrete and geofabric over-layers to support and maintain the horizontal pipe in position. Such additional reinforcements are undesirable in that they are time consuming and expensive to install and require extensive excavation and backfilling as compared to prior retaining wall systems that primarily rely on the horizontal soil anchors alone. However, these horizontal soil anchors cannot provide an additional level of vertically oriented support, as needed for softer soils. Therefore, a retaining wall system that can bear vertical and horizontal loads is needed that can simply and economically provide horizontal anchoring and vertical support for a shoring wall.